The invention concerns a boot for a sport involving sliding motion, in particular, downhill skiing, wherein the upper is constituted, on the one hand, of a plastic shell of a variable volume closing itself over the foot and the instep by two overlapping flaps and provided with at least one closing and tightening device comprising a portion integral with the shell corresponding to the internal side of the foot and an external part of the shell integral with the opposite side, the shell presenting zones of different rigidities and, on the other hand, of a cuff joined to the shell at two opposed points in the malleolar, opening itself toward the front, provided with at least one closing and tightening device and presenting likewise the zones of different rigidities.
In boots having a rigid shell according to the prior art, during the flexing of the leg, the lower buckle of the cuff comes to press against the shell which likewise controls the flexing of the boot.
In patent FR 2 077 184, the content of which is incorporated by reference, the fabrication of ski boots having characteristics as close as possible to boots of leather and utilizing two or more plastic materials having different mechanical properties is proposed. The shell of the boot is formed by successively injecting plastic material with the introduction of reinforcing elements at predetermined points in the injected material.
The resulting shell is, in this way, a relatively supple shell providing reinforced zones for anchoring the buckles of the boot.
In the European Patent Application EP 0 645 101, the content of which is incorporated by reference, a ski boot shell presenting zones of different rigidities and different resistances is known, the more resistant and the more rigid parts constituting a type of triangular framework, wherein the role is the optimum transmission of force between the leg and the ski.
These designs have the purpose of lightening the boot without weakening the anchoring of the buckles and preserving for them a rigidity sufficient for performing its role as an interface between the foot and the ski.
If one considers only the shell and the cuff, the limit for lightening of the shell and the cuff together has been attained if one desires that the boot preserve the flexural characteristics and sufficient rear support.
The invention has the purpose of going beyond these limits by taking into consideration the assembly of the boot, that is to say the shell and its cuff generally referred to as the collar.
The boot according to the present invention is characterized in that the sides of the shell present zones of lesser rigidity permitting the support, on the two sides of the shell, of a rigid heel zone extending toward the front by a lateral oblique band extending at least to the tightening device situated the most forward in such as manner as to carry the tightening device, in that the cuff presents a zone of highest rigidity comprising two lateral flanges/sides, by which the cuff is articulated on which the lateral bands of the shell, and at least a collar connected to the flanges/sides and having a closing device and a tightening device, and in that the rearward portion of the collar is connected to the shell""s heel zone by a joining component resistant to tension and/or compression, of such a type that the oblique band, the collar, and the joining component form a skeleton assuring the kinematics of the boot.
For kinematics, one expects, in particular, the control of the flexing of the boot.
The skeleton fulfills all the mechanical conditions necessary for skiing and it may be reduced to a minimum, watertightness being assured by the portion having the lesser rigidity therefore the thickness may be reduced because this part does not have a mechanical function. The weight of the boot will find itself, consequently, further reduced.
In other words, as opposed to traditional boots which form a whole and react globally, the boot according to the invention have been totally restructured such that each part plays a very precise role: the supple, lesser rigid portion assures watertightness, the rigid part constitutes a skeleton and the joining component which control the of the rear support.
The joining component between the collar and the shell may be a rigid bar or an elastic joint in tension permitting a flexing of the cuff towards the front in a manner to follow the flexing of the leg or also an elastic connection in tension and compression in a manner to likewise absorb the shocks toward the rearward portion.
The joining component may be equally made of a releasing device such as a toggle joint described in patent application WO PCT/US 20203, the content of which is incorporated by reference, having the purpose of protecting the rear crossing ligament.
The shell and the collar is advantageously provided with a process of bi-injection consisting of the successive injecting plastic materials of different rigidity in the same mold or in two successive molds.